Two firefighters were killed in a 9-alarm Back Bay blaze that was “like a blowtorch,” Boston Fire Department officials confirmed during a press conference on Wednesday night.

Lieutenant Edward J. Walsh and Firefighter Michael R. Kennedy were both working to battle the flames in the basement at 298 Beacon St., near the intersection of Beacon and Exeter.

Kennedy, an unmarried 33-year-old who lived in Hyde Park and had over six years of firefighting experience, was recovered alive but with severe injuries, officials said. He was immediately transported to Massachusetts General Hospital, where he was pronounced dead.

(Incident Commander, Deputy Chief Joseph) Finn said Walsh was found near the stairs in the basement of the building. Kennedy was alive when he was pulled from the structure, but later died at Massachusetts General Hospital.

The fire broke out in the basement at about 2:45 p.m. and quickly grew to a nine-alarm blaze — the highest alarm that can be struck in Boston. Within minutes of crews responding, a firefighter trapped in the basement made a mayday call.

Finn said high winds fanned the flames and had a “dramatic impact” on how quickly the fire spread.

“In 30 years, I have never seen a fire travel that fast, escalate that quickly and create such havoc in such a short period of time,” Finn said.

Walsh and Kennedy issued a mayday call a mere two or three minutes after they rushed into the basement, Finn said. He said he believed a window in the front of the building shattered and the wind pushed the fire toward them. One of the doomed firefighters can be heard on haunting dispatch radio recordings frantically calling for more water in their line and saying, “It’s getting hot down here.”

Walsh was pronounced dead at the scene; his brother firefighters recovered his body about 7:45 p.m. — while the top floor of the badly charred building was still in flames — and carried him out the back of the building to an ambulance on Storrow Drive, with fellow jakes forming an honor guard, helmets in hand.

The cause of the fire remains under investigation. A Suffolk prosecutor with special training in fatal fires will investigate alongside Boston police and fire officials, but a spokesman for District Attorney Daniel F. Conley cautioned that the probe “is standard procedure in any unattended or unnatural death; it does not necessarily suggest foul play.”